In recent years, aiming to treat various materials, or for medical applications or the like, studies related to the use of plasma generated by devices on the basis of various discharging principles under an atmospheric pressure environment have been conducted.
Non-Patent Document 1 discloses a conventional arc-discharge type endoscope-mounted plasma device using an RF power source which was developed for medical use. However, this device is configured to pass an electric current to human bodies and hence trigger thermocoagulation caused by resistance heating, generate high energy, and hence may cause tissue damage depending on the usage. In addition, since a discharge path moves to an area having less electrical resistance, the device has various drawbacks in operability. Therefore, even though continuous treatment is intended for the purpose of reliable hemostasis, such continuous treatment is difficult due to an increase in electrical resistance caused by the thermocoagulation. Accordingly, there are problems in both aspects of safety for tissues of human bodies and operability in treatment work.
On the other hand, a conventional device using a dielectric-barrier discharge disclosed in Non-Patent Document 2 is subject to less heat load because it uses plasma at low temperatures (on the normal temperature level), and hence provides a hemostasis approach on the basis of a new coagulant effect principle other than heat, so that advantages such as reduction of load to living bodies are achieved. However, this device has a relatively large treatment surface, and hence there is a problem in operability. In addition, since a human body or an object to be treated serves as the grounding electrode and discharges electricity in the atmosphere, there is a problem in that the electric current tends to flow through the human body or the object to be treated, and a streamer discharge tends to occur. When the streamer discharge occurs, part of the human body or the object to be treated may be damaged.
Further, Patent Document 1 discloses a jet-blow type plasma device using dielectric-barrier discharge. This device is a device central to preparing material or performing surface modification. However, since the device has a structure in which a metallic electrode is exposed to the plasma and also faces a material, the material may discharge by itself depending on the conditions.
As another type, Patent Document 2 discloses a plasma treatment device used for cleaning of foreign substances such as organic substances existing on the surface of a treated substance such as an electronic component or surface modification. This device has an advantage in that glow discharge may be generated stably and uniformly. However, since this device has an internal electrode facing the treated substance, there is a problem in that the electric field intensity with respect to the treated substance is increased and hence an electric current becomes large, the delicately treated substance may be damaged.
Patent Document 3 discloses a plasma treatment equipment which is capable of generating a relatively homogeneous glow discharge and hence restrains generation of a streamer discharge, thereby being capable of reducing damage to the treated substance. However, since this device has an internal electrode covered with a dielectric material facing the treated substance, there is a case where the electric field intensity with respect to the treated substance is increased, and hence an electric current becomes large, so that the delicate treated substance may be damaged. In addition, a gas diffusion panel is mounted and hence there is a problem in that the size of the device is increased.
Patent Document 4 discloses a device configured to arrest bleeding used for the purpose of hemostasis. However, a high-temperature plasma of 4,500 K to 10,500 K or so is generated, and coagulation on the basis of heat is achieved. Therefore, there is a problem in that the surface tissue is carbonized and a necrotic layer is formed.
Patent Document 5 discloses a plasma knife having a configuration in which an electric field intensity with respect to a living body is further increased to enhance hemostasis characteristics for the device disclosed in Patent Document 4. However, because of a configuration in which the electric field intensity is enhanced, there is a problem in that the tissue damage may further be remarkable and serious.
Patent Document 6 discloses a hemostasis device using lower-temperature plasma utilizing microwaves for the purpose of hemostasis. However, according to this device, since the electrode is exposed in the vicinity of the living body and the discharge occurs outside, there is a risk of contact with tissue of the living body. In addition, the material may be damaged when treated therewith. Furthermore, the jet length is extremely short, with a length of 4 mm or so with a power of 5 watts and a flow rate of 2 slm, so there is a drawback in operability.
Patent Document 7 discloses a surgical device configured to generate plasma by an arc discharge between a pair of electrodes and eject plasmatized gas used for performing electrical surgical treatment. However, this device is subject to a high temperature at an electrode portion and there is a problem in durability or the like.
As described above, when discharge energy is high, there is a problem in that the delicate object or substance to be treated, such as in medical use, may be damaged due to the plasma treatment. Therefore, since only weakening energy makes the start of generation of plasma under the environment of the atmospheric pressure difficult, an electrode for generating plasma is provided in the vicinity of the ejection port or so as to be exposed for generating plasma in the prior art. In addition, in the prior art, even though the plasma having weakened energy as described above can be generated once under the environment of the atmospheric pressure, dangerous phenomena such that the treatment conditions change because the plasma is unstable, or the object to be treated may be damaged by the streamer discharge or the like, tend to occur, so that treatment in medical use or the like has been almost impossible. In this manner, low-energy plasma treatment equipment under the environment of atmospheric pressure which allows plasma treatment in the medical field and plasma treatment in an industrial field is strongly expected.